1. Field of the Invention
The present invention relates generally to a fluid-filled cylindrical elastic bushing adapted for damping and isolating primarily a vibrational load applied in its radial direction, and more particularly to improvements in such a fluid-filled elastic bushing which is easy to manufacture, with desired pre-compression of an elastic body and sealing of fluid chambers.
2. Discussion of the Prior Art
A cylindrically bushing adapted to damp and isolate primarily vibrations applied in its radial direction is known as a flexible connector or cushioning device interposed between members of a vibration system, for example, as a suspension bushing for connecting various arms and rods in a suspension system of an automotive vehicle.
A so-called fluid-filled elastic bushing has been widely used as such a cylindrical bushing. An example of a fluid-filled elastic bushing is disclosed in laid-open Publication No. 61-10138 of unexamined Japanese Patent Application, whereby the bushing includes an inner sleeve, an intermediate sleeve which is disposed radially outwardly of and coaxially with the inner sleeve, an elastic body which connects the inner and intermediate sleeves and has a plurality of pockets that are exposed through a corresponding plurality of windows formed through the intermediate sleeve, an outer sleeve which is fitted on the intermediate sleeve and closes the pockets in the elastic body, so as to define a plurality of fluid chambers which are filled with a non-compressible fluid and whose volumes are variable in response to a vibrational load applied between the inner and outer sleeves, and an orifice passage for fluid communication between the fluid chambers.
In the fluid-filled elastic bushing of the type as described above, vibrations having frequencies to which the orifice passage is tuned may be excellently damped and isolated, based on restricted flows of the fluid between the fluid chambers through the orifice passage, or based on resonance of the fluid masses in the bushing.
In the art of manufacturing such a fluid-filled elastic bushing, a unitary intermediate product is prepared in a vulcanization process, such that the elastic rubber body is secured by vulcanization of a rubber material, to the outer surface of the inner sleeve and the inner surface of the intermediate sleeve. On the other hand, the fluid chambers are sealed by providing a sealing rubber layer between the outer surface of the intermediate sleeve and the inner surface of the outer sleeve. Where the sealing rubber layer is formed integrally on the outer surface of the intermediate sleeve, the sealing rubber layer tends to be damaged or separated from the intermediate sleeve when the intermediate sleeve is radially inwardly drawn for radially inward pre-compression of the elastic rubber body, which is effected for the purpose of eliminating stresses in the elastic rubber body due to its shrinkage during the vulcanization process, and improving the adhesion of the rubber body to the inner and intermediate sleeves.
For accomplishing the sealing of the fluid chambers and the radially inward pre-compression of the elastic body, the vulcanization of the elastic body and the vulcanization of the sealing rubber layer are conventionally effected in two independent steps. Further, the intermediate sleeve is first radially inwardly drawn for pre-compression of the elastic body, and then the outer sleeve is radially inwardly drawn for securing fluid tightness between the outer and intermediate sleeves, i.e., fluid tightness of the fluid chambers which are defined by the elastic body and the outer sleeve.